Method and medium for electron beam recording



Jufly 111, 1967 w, J. PLANK, JR 333319077 METHOD AND MEDIUM FOR ELECTRON BEAM RECORDING Filed Dec. 28, 1964 INVENTOR.

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United States Patent 3,331,077 METHOD AND MEDIUM FOR ELECTRON BEAM RECORDING William J. Plank, In, White Bear Lake, Minn., assignor This invention relates to a new and very useful storage medium suitable for direct electron beam recording and subsequent direct optical read out which employs an electron sensitive layer as its information storage component and which employs an alkali soluble metal layer as its removable electrically conductive layer adapted to dissipate electrons during an electron beam recording operation.

Although various constructions have been proposed for direct electron beam recording using an electron sensitive layer, it is believed that no one has heretofore used in such a construction as the removable electrically conductive layer a thin deposited layer of a metal such as aluminum or copper coated upon one face of the base support layer of such medium construction.

Such a medium during a recording operation dissipates electrons so as to maintain the electrostatic charge potential at a level which is so low as not to affect appreciably the medium or the recording electron beam. During recording the metal layer can be grounded.

When such a medium construction following exposure to an electron beam is placed in an alkaline solution, the layer of metal is chemically completely dissolved in such solution and thereby removed conveniently and quickly. The result is that the recorded and processed medium is then optically clear (not light absorptive) as respects its capacity to transmit light therethrough in unimaged areas (in the case of positive recordings) or optically clear in imaged areas (in the case of negative recordings).

An object of this invention is to provide a sheet-like electron beam recording medium which employs an electron sensitive layer, a base support layer, and a chemically dissolvable electrically conductive layer.

Another object of the present invention is to provide in an electron beam recording medium of the class indicated an electrically conductive metal layer which is completely dissolvable in alkaline aqueous solution.

Another object of this invention is to provide an electron beam recording medium construction which is adapted to dissipate electrons during a recording operation at such a rate of conducting sulficient electrons during a recording operation that there is substantially no elfect upon a scanning modulated electron beam accomplishing recording and no deleterious effects upon such medium.

Another object of this invention is to provide a method for directly recording under vacuum conditions the information associated with a modulated electron beam and for subsequently directly reading out such recorded information by direct optical projection (i.e. transmission) techniques.

Another object is to provide a method for removing an opaque or partially opaque conductive layer from an electron beam recording medium by chemical dissolution so as to make such medium suitable after recording for readout by optical projection techniques.

Other and further objects of this invention will become apparent to those skilled in the art from a reading of the present specification taken together with the drawings wherein:

FIGURE 1 is a vertical cross-sectional diagrammatical view of an embodiment of an electron beam recording medium of this invention before a recording operation; and

FIGURE 2 is a view of the embodiment of FIGURE 1 after the same has been exposed to a modulated scanning electron beam and developed by a conventional silver halide photographic development process.

As can be seen by reference to FIGURE 1, one embodiment of a sheet-like storage medium of the present invention employs a film base layer 10 which is generally subbed on one face thereof by a thin subbing layer 11.

Over the subbed film base layer is coated a photographic silver halide emulsion layer 12. Although not shown, it is often times convenient and indeed is preferred for purposes of this invention to coat the electron sensitive layer, for example, a photographic silver halide emulsion layer 12 with a top coat layer of clear gelatin which serves to protect the layer 12 during handling and storage and does not interfere with the development thereof following exposure. The reverse face of the film base layer 10 is coated with a thin layer of metal, preferably aluminum or copper. This layer is designated in its entirety by the numeral 15 and will hereinafter be described more fully. As the film base or support layer 10, there is employed an optically clear dimensionally stable material having opposed parallel anchorable faces and an appropriate outgassing coefl'icient.

The base support layer, the electron sensitive layer and the conductive layer will now be described. Because electron beam recording operations are generally carried out under relatively high vacuum conditions, it is desirable though not necessary to use materials in the medium constructions of this invention which are vacuum stable. It is also desirable though not necessary in making medium constructions of this invention to employ materials which have minimal residual quantities of volatilizable gases, liquids, and solids associated with them because such materials when released in vacuum during electron beam recording operations can interfere with the operation of the electron gun, especially its electron emission sources, as those skilled in the art will readily appreciate.

As the base support layer there is employed an optically clear, dimensionally stable material having opposed, parallel anchorable faces.

For purposes of this application, the term optically clear has reference to even and high (eg more than 50%) light transmission in the visible region of the spectrum.

The term dimensionally stable has reference to the fact that a material in a medium undergoes no appreciable changes in its dimensions under any of the (vacuum) recording, processing, storage and readout conditions to which such medium is to be subjected (i.e. such medium is not rendered inoperable by reasons of dimensional changes in its support layer).

The term anchorable faces or simply anchorable has reference to the fact that the base support layer is capable of having other substances chemically or physicochemically fastened or bonded to either one or both faces thereof so as to form initially a composite, integral structure, depending upon the layers used, and their positions in a given medium construction. Thus, such a base support layer may be subbed, primed or the like before being used in a medium construction of this invention.

As those skilled in the art will appreciate, it is necessary to employ as the base support a material which is capable of having other substances anchored to either one or both faces thereof. Preferably the base support is constructed of a film-forming organic polymer. A suitable thickness for the base support layer is from about 0.25 to 10 mils.

An especially preferred base support material is poly ester film, such as that type technically known as polyethylene terephthalate film. Other suitable base support materials useful in the construction of sheet-like storage media of the present invention are polycarbonates, cellulose esters, polystyrenes and the like.

As the electron sensitive layer there is employed a composition capable of developing therein, following exposure thereof to excited electrons, internally changed regions corresponding to, or representative of, the excited electrons striking such regions. Such regions are detectable (observable) by means of the passage or transmission of light energy (i.e. energy having wavelengths of from about 400 to 700 millimicrons) therethrough because such light energy is selectively or differentially transmitted by such regions compared to the adjacent regions.

It will be appreciated that such regions are in an image wise pattern of either a positive or negative character, depending upon recording conditions and nature of the particular electron sensitive material used 'as well as upon the processing applied.

The electron sensitive composition is further characterized by the fact that when in a layered form within a medium construction of this invention, even the inherent limited power of excited electrons (i.e. those derived from a modulated electron beam) is sufficient to enter such layer and affect the desired exposure thereof so as to produce an image-wise recording of those excited electrons. While there are many ways, as those skilled in the art will appreciate, to effect this result, it is achieved in the present invention by controlling the uniform distribution of electron sensitive elements in the electron sensitive composition in such a way as to make a layer of such composition in a medium construction as thin as practicable and yet achieve maximum change in the electron sensitive layer during the beam dwell time upon a given surface area of such medium.

sired changes in an electron beam exposed, electron sensitive composition.

The term dwell time as used in this application has reference to the average time, as for instance, in microseconds the spot diameter formed by a moving electron beam spends in an area equal to its own.

The term element as used in this application has reference to a functional component of the electron sen sitive composition which may consist of a homogeneous mixture or chemical combination of one or more chemical entities.

In general, such electron sensitive compositions are well known to those skilled in the art. For convenience and reference purposes, various classes of these imaging materials are summarized in the following Table I. In this table, the term imaging process has reference to the manner in which an image is formed by a physical or chemical change in a given medium construction. Exposure is generally prolonged until the image material has undergone a change sufficient to effect the desired recordation of information. The term development has reference to a particular chemical or physical process by which the change or alteration in image material created during exposure to electron radiation is detected and amplified. Development may (a) require a second, separate, and subsequent processing step following exposure or (b) occur simultaneously with, or as a direct and dependent consequence of, exposure to electron radiation. The term fixing has reference to a process step subsequent to development which produces desensitization of areas in 'an image material to subsequent or further exposure to actinic radiation. Depending on the nature of the phenomena utilized, development and/or fixing may not be necessary, may be eliminated, or may even be For purposes of this invention it is generally conaccomplished simultaneously with one another.

TABLE I.FUNCTION DESCRIPTIONS OF IMAGING PROCESS STEPS WITH DIFFERENT IMAGING SYSTEMS I. Imaging Process 11. Development III. Fix IV. Process 1, Destroy a reactant Chemical reaction forming a vlsiby distinct Not needed Diazo-Bruning, Ozalid} product in non-exposed areas. 2. Photodecomposition producing Heat to expand gas within softened film pro- Exposure to uniform photon Vesicular Diazofi gaseous products in a thermoplastic bly distinct product.

image.

ducing light scattering bubbles.

Heat sensitive physical or chemical change to produce a visibly distinct product. Transfer and chemical reaction to yield a visi- Conversion of basic dye to acid form Photochromatic (conversion of one chemical species to different chemical species). Synthesis of photon absorbing material Chemical amplification of the exposed latent energy.

Background is heat sensitive Chemical removal of un- Photo ra h developed silver halide. g p y 1 [7.8. Patents Nos. 2,829,976; 2,807,545; 2,755,185; 2,774,669; 2,691,587.

2 U.S. Patent No. 2,740,896.

a British Patents Nos. 844,077; 844,079; 844,256; Niepce de St. Victor, Photographic News 2 (1859). 4 Y. Hirshberg, J. Chem. Phys. 27, 768 (1957); South African Patent No. 61,861; French Patent No. 1,272,059; Belgian Patent No. 607,355; British Patents Nos. 887,958;88,902, 883,803; 11.8. Patents Nos. 3,090,687; 3,038,812; 3,020,171; 2,953,454; 3,022,318.

venient and satisfactory to employ an electron sensitive composition which when deposited in a layered form upon an inert surface to a thickness of about 2; (microns) will develop an optical density of at least one when ex posed to not more than 10 electrons per square centimeter of layer sufrace area when accelerated to penetrate substantially all of the sensitive layer. r a

The optical density (D) of an 'e'lectron'sensitive layer deposited in a medium construction of this invention is defined by the relation D=log 0 where O is the opacity. If I and I are the incident and transmitted intensities respectively, the opacity is given by 1 I Optical clarity can be measured as the reciprocal of the opacity or 1/1,.

It will be appreciated that the term develop, developing or equivalent as used in this context may or may not involve subsequent chemical or physical processing following a recording operation so as to produce the de- U.S. Patent No. 3,042,515, R. H. Sprague and M. Roscow Photo Sci. & Eng. 8, 91 (1964); R. H. Sprague and It. L. Fitchte lbid 95- U.s. Patent No. 3,102,029. r p

gisfkPgtent gtp.t2,950,1l?4. Ch

a i es o ograp ic emistr volumes 1 and 2 bli he by Fountain-Press (London, 1958). y DU 5 d .The conventional diazo processes mentioned in Table I involves production of a colored azo dye. Exposure to excited electrons of a stabilized =diazonium compound destroys its ability to react with a coupler and hence produce -a dye. In the unexposed areas the dye-forming reaction occurs readily upon the addition of an alkaline material (ammonia vapor) if the diazo system already contains a coupler component or both an alkaline material and coupler.

In the so-called vesicular diazo process mentioned in Table I, exposure to excited electrons decomposes a diazonium salt dispersed in a thermoplastic binder. When the medium is subsequentlyheated, the nitrogen produced by the decomposition expands in the softened binder producing a vesicular, light scattering image in the exposed areas.

In Example 4 of Table I selective surface absorption or selective deposition can be used to create a differential chemical pattern of an imaging system component corresponding to that on the original graphic master. If the tinctorial power of the reaction product is high, or if the transferred material is a reaction catalyst, transfer of only very small amounts of material can provide a visible image. Thus, some degree of amplification may be possible.

For some time it has been known in the arts that upon exposure of highly halogenated polymers such as polyvinyl chloride or polyvinylidene chloride to excited electrons one obtains acidic reaction products generated in the polymer matrix, directly as a result of the irradiation. If in such a polymer matrix there is incorporated the basic form of an acid-sensitive dye such as one of the commonlyknown indicator dyes such as phenoph-thalein, then,

upon exposure and generation of the acid component in the matrix, a color change is produced in the irradiated areas.

Photochromic materials are well known in the photochemical art. Such materials, when exposed to excited electrons, undergo a structural rearrangement which results in the formation of a differently and usually more colored species, compared to the initial color. A wide variety of such compounds are included in the chemical class known as benzoindolinopyranospirane. The National Cash Register Company-developed photochromic imaging system utilizing this general technology for the recording of grain-free microimages can be employed in making the electron-sensitive layer in media of this invention.

The exposure to excited electrons of highly halogenated alkanes, such as carbon tetrabromide, bromoform, or chloroform produces a highly chemically reactive radical. When, for example, a substituted aroma-tic amine is incorporated in close proximity thereto, upon subsequent heating an image is formed. The literature discloses that Horizons, Incorporated, has made practical utilization of this color forming reaction in preparation of electron-sensitive compositions. These compositions, when suitably layered in combination with fluorescent composition, can be used in electron-sensitive layers in media constructions of this invention.

Example 5 of Table I utilizes a dehydrohalogenation electron-sensitive system which employs a combination of two components: an acid sensitive indicator and a highly halogenated polymer. The acid sensitive indicator is capable of changing color at pH below about 7 when the highly halogenated polymer is capable of liberating an acid component. The halogenated polymer is normally solid and has a molecular weight of at least about 1,000 and further has at least 25% of labile halogen selected from the group consisting of chlorine and bromine. The indicator is generally homogeneously distributed throughout the halogenated polymeric binder, and is preferably dissolved therein. It may also be provided as a localized coating or be concentrated in the top surface of the polymeric binder in a particular medium construction. Preferably the polymers are soluble in conventional organic solvents. Solubility, of course, can be adjusted to some extent by employing copolymers, a balance being achieved between halogen content and copolymer solubility. Vinylidene chloride copolymers with such monomers as the aliphatic acrylates (e.g. n-butyl acrylate, methyl acrylate, ethyl acrylate, he-xyl acrylate, methyl methacrylate, betachloroethyl acrylate, etc.), acrylonitrile, vinyl chloride, vinyl acetate, vinyl butyrate, etc. are preferred highly halogenated polymer systems. Ethylenically unsaturated monomers with a high halogen content, such as 1,1,33,3- pentachloropropene-l, fluorotrichloroethylene, 1,1-difluoro-2,2-dichloroethylene, tri-chloroethylene, etc. copolymerized with vinyl or vinylidene chloride or bromide or with aliphatic acrylates can also be employed. Halogenated aromatic polymers are considerably less effective than the halogenated aliphatic polymers, although the copolymerization of a suitable halogenated aliphatic monomer with an aromatic monomer (e. g. styrene, vinyl toluene,

6 vinyl carbazole, etc.) selected for its solubility characteristics is suitable.

Although the halogenated polymers are desirably deposited from a solution as a film on a surface, they may also be deposited from a latex or intimate dispersion. With those polymers which tend to decompose slowly in the presence of ordinary light and atmospheric oxygen, antioxidants and other stabilizers may be added to improve good storage life.

Since the highly halogenated polymers serve as a relatively non-volatile source of hydrohalic acid, no other brominated or chlorinated compounds which liberate acid under electron beam exposure are required for electron beam imaging.

An electron sensitive composition for use in media of this invention can be prepared by mixing a minor amount of the acid sensitive indicator system with a solution of the highly halogenated polymer and backing. If a transparent imaging material is desired, it will be appreciated that many of the highly halogenated polymers are made more relatively light transmissive in the form of a thin film. For each equivalent weight of acid sensitive indicator from about 1 to about 1000 acid equivalents of the halogenated polymer are employed, although the ratio of these ingredients varies with the particular indicator system, and its acid sensitivity, which is employed. Other additives, e.g. plasticizers, oxidizing agents, etc. may be incorporated into the actinic radiation sensitive coating (preferably such additives are chosen so as not to liberate acid under the actinic radiation). Additional films or coating may be provided on the actinic radiation sensitive layer to protect it from abrasion, etc., provided the-y are relatively transmissive to the electron beam.

With electron sensitive compositions such as just described, a color change therein is generally observed immediately after exposure to excited electrons or shortly thereafter upon subsequent exposure to air thereby providing a visible imaging record in a layer of such a composition. In some instances, when the acid sensitive indicator is reversible, as with the acid-base indicator dyes, the image can be erased by heating the electron sensitive composition to about C. to C. for approximately 30 seconds, the color change being probably due to the volatilization of the acid and an increase in efiective pH of the electron sensitive composition. Erased electron sensitive compositions of this type can be re-used for recording with electron beams although subsequent depletion of the polymeric acid source eventually reduces the efiiciency of recording.

It is sometimes convenient to leave the indicator out of a highly halogenated polymer film initially. Then after exposure of such film to actinic radiation, the liberated acid in the imaged (exposed) areas can be subsequently developed by contacting the exposed surface of the highly halogenated polymer with the acid sensitive indicator system. A separate development roller or bath may be used for this post development step or a second medium construction incorporating or carrying the indicator can be physically brought into contact with the exposed surface of such medium. Such a post development procedure using an acid indicator containing film can be used to prepare multiple copies.

A simple standard test procedure to assist in the selection and definition of highly halogenated polymers and indicator systems useful in such media of this invention employs ultra-violet light. The procedure is to add to a film-forming halogenated polymer 5 milligrams of Congo Red A to 1.0 milliliter of a 20 weight percent solution of such polymer, in a suitable solvent such as tetrahydrofuran. This solution is then knife coated onto a cellulose acetate, polyethylene terephthalate or glass backing to provide a dry film of 0.1 mil thickness. A sample of this dry film is placed at a sufiicient distance from an ultraviolet light source to provide about 0.08 Watt per square centimeter of radiant energy of 2000 to 3000 angstroms wavelength. The sample is irradiated for a period from 2 to 30 seconds. Generation of a blue color indicates a halogenated polymer containing labile halogen useful in the electron beam recording media of this invention. The same standard test procedure is modified for selection of a suitable acid sensitive indicator by using a 20 weight percent solution of vinylidene chloride-acrylonitrile copolymer (90/10 rnol ratio) and 5 milligrams of the acid sensitive indicator system, a strong color change after the ultra-violet exposure indicating a useful indicator for the electron beam recording media.

An especially preferred type of electron sensitive composition comprises silver halide emulsions.

As the photographic silver halide emulsion layer for use in the present invention, one can employ virtually any silver halide emulsion since such emulsions are generally sensitive to electron beams. However, it is greatly preferred for purposes of producing sheet-like storage media of the present invention to use emulsions which are particularly useful for electron beam recording. For the purpose of constructing media of this invention, it is desirable to use fine grain emulsions, that is, emulsions having an average grain size less than about 0.5 micron.

In a given medium construction the thickness of the silver halide emulsion is largely dependent upon the quantity of silver per unit of area which is to be used for recording. Typically, the layer of silver halide emulsion contains from about 5 to 50 milligrams of silver per square decimeter of surface area.

A preferred silver halide emulsion for use in medium constructions of this invention is one which has an average grain size of less than 0.5 micron and a silver-to-gel ratio of about 1:1.

It is sometimes convenient in fabricating medium constructions of the present invention to overcoat the electron sensitive layer with a top coat, particularly when such emulsion layer constitutes the uppermost or bottommost exposed portion in a completed medium construction. As a top coating material one can employ a thin layer of gelatin, say, one less than about 0.5 micron in thickness. Such a layer does not interfere with the development of, for example, silver halide emulsion, following a recording operation and serves to protect the recording medium against accidental abrasion and dust particles during a recording operation as well as during subsequent storage following development.

In order to achieve a good anchoring between the base support layer or material and the particular silver halide emulsion, it is sometimes desirable to employ a very thin layer or layers of a subbing composition to the surface of the base support layer before the same is coated with an electron sensitive layer. Subbing compositions are known and understood to those skilled in the art. Conventional subbing agents for silver halide emulsions, for example, are listed in Glafkides Photographic Chemistry, volume I, pages 467-469.

As the removable electrically conductive layer in a medium construction of this invention there is employed a layer or stratum of metal having a resistivity of not more than about ohms per square (and preferably not more than about 10 ohms per square) as measured in a vacuum of about 10* mm. Hg. This metal layer is selected from the group consisting of aluminum, and copper, and is so positioned in a medium construction as to be in contact with one face of the base support layer. Because the base support layer itself is essentially and conveniently electrically non-conductive, this metal layer is deposited by means of vacuum vapor deposition techniques using the procedures known and used by those of ordinary skill in the art. In general, this layer of metal having the resistivity indicated will have a thickness in the range of from about 10 to 200 A. though thickness greater or smaller than this can be used depending upon (a) the optical clarity of the base support layer, and (b) the image quality of information developed in the electron sensitive layer.

To effect removal of the metallic conductive'layer by immersion of or contact of a medium construction into or with an aqueous alkaline solution as indicated above, the following variables are taken into consideration:

(1) Temperature: As those skilled in the art will appreciate, temperature extremes and extreme temperature changes are undesirable. For example, in the case of silver halide emulsions coating development the temperature of the aqueous alkali removal bath should be equal to the subsequent processing solutions, say, about 68 F. In general, a temperature in the range of 55 to 75 F. is satisfactory.

(2) Solution concentration: A preferred range of pH values is from about 7.5 to 10 (e.g. equivalent to about an 0.01 N to 0.1 N NaOH solution).

(3) Time in solution: In general, it is preferred to have a complete dissolution of the metal layer take place in less than one minute, and, more preferably, in less than about 30' seconds.

In the case of copper conductive layers it is generally desirable to have dissolved in the alkaline solution an oxidizing agent, or a complexing agent which is adapted to solubilize copper, as those skilled in the art will appreciate. For example, when one is using a medium of the invention wherein the electron sensitive layer is formed of a silver halide emulsion, ordinary photographic developer solution will dissolve a copper conductive layer.

The desirability of incorporating a conductive layer into a recording medium of the invention comes about from the fact that the presence of an electrostatic charge during recording impairs sharpness, resolution and accurate positioning of the recorder image. The aforementioned electrostatic charge is built up in the electron sensitive layer or any other insulating layer placed in the first order of electron impingement. This charge can adversely affect the performance of a recording medium, As shown in FIGURE 1, in one embodiment of the invention one exposed face of a base support layer 10* is composed of an electron sensitive layer 12, such as a silver halide emulsion, while the other face thereof is composed of the conductive layer 15.

Another constructional arrangement is to position the conductive layer between the silver halide emulsion layer and the base support layer. Under these conditions the conductive layer is subbed before application of the silver halide emulsion layer thereto. In general, in medium constructions of this invention the conductive layer is positioned on one face of the base support layer.

Characteristic properties of media of this invention depend not only upon the nature of the starting materials but also upon the manner in which a particular medium construction is assembled, aside from recording the development conditions.

Usually the layers arekept distinct one from the other in a medium construction. While adjoining layers need bear no special relationship to one another, it will be appreciated the electron sensitive layer should preferably be so located with relationship to the exterior surface of a given medium construction so as to facilitate or minimize any chemical or physical processing of that medium following exposure thereof to a modulated electron beam. Preferred medium constructions in general are flexible and thin so as to have thickness flexibilities like those of the same order commonly associated with conventional photographic films and magnetic tapes thereby permitting the use of conventional tape transport mechanisms, film sprocket drives, and handling pro cedures generally.

It will be appreciated that in a given medium construction of this invention, the total thickness of, and the interrelationship between layers thereon is such that, immediately after a recording operation, the charge in volts remaining E, the charge in coulombs remaining q, and the distance d between adjacent faces of said electron sensitive layer and said removable conductive layer is such that where k is a proportionality constant characteristic of a given medium construction under a given set of recording parameters. If E is too large, then there are the possibilities of (a) excessive arcing between the electron sensitive layer with the result that fogging of the recorded image can occur, (b) the recording modulated electron beam is deflected in adjacent areas so that accurate positioning of the beam with respect to the medium is lost in recording, and (c) the medium is physically attracted by electrostatic forces to surrounding or adjoining surfaces to such an extent that the medium becomes difficult to handle (i.e. transport) in the recording equipment.

Such layer interrelationship and medium total thickness considerations depend not only upon the nature of the starting materials but also upon the manner in which a particular medium construction is assembled, aside from recording, processing, and readout conditions.

Usually the layers are kept distinct one from the other in a medium construction. While adjoining layers need bear no special relationship to one another, it will be appreciated the electron sensitive layer should be so located with relationship to the exterior surface of a given medium construction so as to facilitate any necessary or desirable development of that layer following a recording operation. It is preferred to keep the electron sensitive layer as close as possible, consistent with the type of construction desired and with the materials of construction being used, to the conductive layer so as to keep d as small as possible relative to q in a given construction. Preferred medium constructions in general are flexible and thin so as to have total thicknesses of the same order of magnitude commonly associated with conventional photographic film and magnetic tapes so as to permit the use of transport mechanisms similar to those used in magnetic tape recorders and motion picture equipment, and handling procedures generally.

An especially preferred class of medium constructions within the teachings of the present invention are those capable of recording information in a high density manner, that is to say, capable of recording information at a bit density greater than about 10 bits of information pe square centimeter of surface area.

In the case where the metallic, conductive layer is positioned between the electron sensitive layer and the base Support, the electron sensitive layer must have the property of being permeable to an alkaline aqueous solution so that the conductive layer can be dissolved and thereby removed by said solution during a time of less than one minute and preferably 30 seconds without affecting:

(a) the optical clarity of the base support, and (b) the image quality of the electron sensitive material.

Media constructions of this invention can be prepared by any convenient, conventional procedure. For example, to make a construction of FIGURE 1, one can begin with a preformed optically clear base support layer. Then one face of such layer can be subbed and coated in turn with a layer of electron sensitive composition or the base support can be purchased already subbed on one or both sides. Finally, the removable conductive layer can be coated upon the opposed face of the base support layer. Except for the conductive layer, the various coatings can be applied as solutions or slurries of composition in a volatile liquid using knife, roll, or similar coating procedures. After application, a coating may be dried before another layer is coated.

Electron sensitive compositions do not constitute in themselves any part of this invention but rather are known to the art, no detailed explanation or description of such treatments is considered necessary or desirable herein beyond that already given above in reference to Table I.

To use a medium construction of this invention, one exposes same to a modulated, electron beam under vacuum conditions making sure that the conductive layer is grounded during such beam exposure. As the techniques of electron beam recording are well worked out and form no part of this invention, no detailed explanation thereof is given herein. However, for illustrative purposes, it is noted that a typical conventional electron beam recording operation may utilize an electron beam characterized by having a beam diameter of from about 1 to 25 microns, a voltage of from about 10 to 30 kv., a current flow of from about 10- to 10 amps and adapted to scan a target area at such a rate that the dwell time is from about 10 to 10- seconds. Vacuum pressures commonly range from 10- to l'() torr.

After such a recording operation the conductive layer is removed from the so exposed medium construction by dissolution using conditions as explained above. Also, any necessary or desirable chemical or physical treatment of the electron sensitive layer, as, for example, to develop a latent image when this layer is a silver halide emulsion. As such chemical or physical treatment is a characteristic associated with the particular type of electron sen sitive composition employed in any given medium construction, and as such chemical or phyhical treatment involves procedures well known to those of ordinary skill in the art and form no part of the present invention, they are not described in detail herein.

After processing the resulting medium can be read out by optical projection (trans-mission) techniques. For example, the medium can be then placed in a conventional photographic projector and projected on a white surface.

FIGURE 2 illustrates in cross-sectional diagrammatic fashion the appearance of the medium construction of FIGURE 1 after a recording and development operation. Unless otherwise indicated, the parts of the construction of FIGURE 1 are the same as in FIGURE 2 except that prime marks are added.

The imaged areas can be in many different forms depending upon exposure during a recording operation. Observe that there is no conductive layer in the construction of FIGURE 2.

The invention is further illustrated by reference to the following specific examples. Unless otherwise indicated, the term parts as used in these examples refers to parts by weight.

EXAMPLE 1 A flexible transparent film of polyethylene terephthalate (available as Type A, 500 gauge, Mylar from E. I. du Pont de Nemours and Company in Wilmington, Delaware), which is provided with a subtratum to make aqueous coatings adhere to it on one side, is vapor coated on the nonsubbed side with an aluminum layer, approximately 60 A. in thickness and a light-transmission of approximately 50%. The electrical resistance of this layer is about 2000 ohms per square.

A silver halide emulsion is prepared according to principles described in Glafkides Photographic Chemistry, volume I( pages 341-353. The resulting emulsion contains 3.5% silver, a silver-to-gelatin ratio of 1:1 and a mole ratio between silver bromide and silver chloride of 12 to 88. The emulsion contains all the necessary coating finals known to those skilled in the art, and as described in Glafkides Photographic Chemistry, volume 1, chapter 21, pages 369-389.

The substrate is prepared according to the teachings of British Patent No. 552,085 (1943).

The emulsion is now coated on the non-aluminum vapor coated but subbed side of the polyester film, on a photographic film coating machine equipped with an extrusion applicator. The coated emulsion layer after drying is approximately 2.5 microns thick and contains approximately 25 milligrams of silver per decimeter squared.

The emulsion preparation, coating and the subsequent steps, are carried out under red photographic type illumination only.

The emulsion is supercoated with a protective gelatin layer of approximately 0.5 thickness. Layers of this type and their preparation are described in P. Glafkides Photographic Chemistry, paragraph 359, volume 1, pages 386 and 387. n

This film construction is now slit into film strips of 16 millimeter width and perforated. The medium is now used for exposure by electron beams as follows:

The medium is mounted into a 16 millimeter motor driven sprocket drive tape transport mechanism and guided under an electron beam in a vacuum chamber under a vacuum of about 5 10 mm. Hg. The axis of rotation of the sprocket is parallel to the direction of deflection of the electron beam so that the plane of film movement is effectively perpendicular to the direction of deflection. Film or tape speed is about 9 inches per second.

A conventional television-type horizontal deflection is used to deflect the electron beam. The horizontal deflection is accomplished by driving the deflection coil on the electron gun with a 15,750 cycles per second sawtooth current. The sawtooth has a scan period of about 53.5 microseconds and a retrace period of about 10 microseconds. The resultant horizontal deflection of the electron beam is set for about 1 centimeter width at the surface of the media.

The electron beam is about 10 microns in diameter at the surface of the media and has an acceleration of about 15 kilovolts. The beam current is intensity modulated by applying a modulating voltage at the electron gun grid. The intensity modulation of the beam corresponds to the information to be recorded. The peak beam current under such modulation is about .1 microampere.

The media and electron gun are mounted in a vacuum chamber held at about 5X10 mm. Hg pressure.

The recording takes place by simultaneously moving the film or tape and deflecting and modulating the electron beam so that a scanned line-like latent image pattern of the information results.

After recording and removal from the vacuum, the exposed medium is inserted for 30 seconds in a 0.01 N

- aqueous sodium hydroxide solution, whereby the aluminum dissolves and dissociates from the support as is indicated by the subsequent transparency of the base support and loss of medium conductivity in vacuum. It is removed and then developed in a developer of the following composition for one minute at 68 F.:

Water cc 500 p-Methylaminophenol sulfate grams 2.2 Sodium sulfite do 96.0 Hydr-oquinone do 8.8 Sodium carbonate, monohydrate do 56.0 Potassium bromide do 5.0

Add cold water to make 1.0 liter.

An equivalent developer is commercially available as Kodak D-l9 developer, manufactured by Eastman Kodak Company. After development the media is rinsed in water at about 68 F. for about 30 seconds and transferred to a fixing bath at about 68 F. for about 2 minutes. Composition -of the fixing bath is as follows:

Water F., at time of mixing) cc 600 Sodium thiosulfate (hypo) grams 240.0 Sodium sulfite, desiccated do 15.0 Acetic acid, 28% pure cc 48.0 Boric acid, crystals grams 7.5 Potassium aluminum (aluminum potassium sulfate) do 15.0

Add cold water to make 1.0 liter.

An equivalent fixer is commercially available as Kodak Fixer for films, plates, and papers as manufactured by Eastman Kodak Company.

After fixing, the media is washed in water at about 68 F., for about five minutes. The media is then removed and allowed to dry.

For retrieval (readout) of the recorded information the film media is positioned in a 16 millimeter movie projector and projected against a white surface.

Instead of using a silver halide emulsion as the electron sensitive layer, one can employ another type of electron sensitive composition in place thereof, such as each of those listed in Table I above. Such other electron sensitive composition is then deposited in layered form in a medium construction just described. Then when the resulting medium is used for electron beam recording and thereafter processed to remove the conductive backing before read out, faithful reproduction of recorded information is similarly achieved on readout.

EXAMPLE 2 A base support of cellulose triacetate of about 5 mils in thickness (Eastman Kodak) is vapor coated with a copper layer on one side. This copper layer is about 60 A. in thickness and has a light transmission of about 50%. The copper layer is then subbed with a substratum layer which is prepared and applied in accordance with the teachings of P. Glafkides in Photographic Chemistry, volume I, page v469. Finally over the subbing layer is coated a silver halide emulsion followed by a gelatin overcoat, all as described in Example 1. The medium is then slit, perforated and subjected to a recording operation as in Example 1.

After removal from the vacuum recording chamber, the exposed medium is then developed as in Example 1.

During the time of development, and in the development alkaline medium the metallic layer is dissolved.

The remaining processing steps and then readout are accomplished as in Example 1; excellent fidelity of recording is observed.

When this same backing with its copper vapor coat and subbing is coated with an electron sensitive material comprising a diazo Bruning system in a gelatin carrier is slit, perforated and subjected to a recording operation, and is thereafter processed to remove the copper layer in the manner described in Example 1, it is observed that high fidelity of recording is achieved.

I claim:

1. In a method for direct electron beam recording of information in a sheet-like recording medium adapted for subsequent readout of prerecorded information by optical projection, said medium containing a base support layer, an electron sensitive composition layer, and a conductive layer positioned adjacent one face of said support layer and composed of metal, the improvement which comprises the steps of:

(a) exposing under vacuum one surface of such a medium to an electron beam modulated with information to be recorded while simultaneously grounding the conductive layer of such medium, said beam having an associated energy and relative motion adapted for recording such modulation in the electron sensitive composition layer of such medium, and a (b) thereafter contacting said conductive layer with an aqueous alkaline liquid for a time suificient to dissolve and thereby remove such layer from such medium.

2. A sheet-like storage medium adapted to (a) develop therein an image pattern corresponding to information associated with a modulated electron beam when such a beam scans one face thereof during a recording operation, 1

(b) dissipate electrons during such an electron beam scanning operation, said dissipation being at a rate sufiicient to maintain the electron potential associated therewith in said medium at a level with substantially does not adversely affect the recorded image,

(c) be processed after such recording operation and before readout by conventional optical transmission techniques so that the imaged areas selectively modulated transmitted light,

said medium comprising in combination (a') an optically clear, dimensionally stable, base support layer having opposed parallel anchorable faces,

(b) an electron sensitive layer composed of an electron sensitive composition which, when deposited in a layered form upon an inert surface is characterized by having the chemical capacity to develop an optical density of at least one when exposed to not more than electrons per square centimeter of layer surface area, when said electrons are accelerated to penetrate substantially all of this sensitive layer.

(c') an electrically conductive layer composed of metal and characterized by (1) having the capacity to be chemically substantially completely dissolved in an alkaline liquid medium from the remainder of said medium without appreciably affecting at time of removal:

(a) the optically clarity and physical stability of the base support layer, and

(b") the image quality of information developed in said electron sensitive layer,

(2) being so positioned in said medium as to be in contact with one face of said base support layer,

(d) the relationship between said base support layer,

said conductive layer, and said electron sensitive layer being such that when said conductive layer is positioned between said base support layer and said electron sensitive layer, said electron sensitive layer is permeable to alkaline aqueous solutions so that said conductive layer can be so dissolved.

3. The medium of claim 2 wherein said conductive layer has a resistivity of not more than about 10 ohms per square in a vacuum of about 10 mm. Hg.

4. The medium of claim 2 wherein said conductive layer is positioned on the face of said base support layer opposed to that on which said electron sensitive layer is positioned.

5. The medium of claim 2 wherein said base support layer is a polyester film.

6. The medium of claim 2 wherein said base support layer is a cellulose ester film.

7. The medium of claim 2 wherein said electron sensitive layer is a silver halide emulsion.

8. The medium of claim 2 wherein said conductive layer is aluminum.

9. The medium of claim 2 wherein said conductive layer is copper.

References Cited UNITED STATES PATENTS 2,664,043 12/1953 Dalton 346-435 X 3,142,585 7/1964 Katchman 117211 3,185,995 5/1965 Dickens 3461 3,196,011 7/1965 Gunther et a1 96-1 RICHARD B. WILKINSON, Primary Examiner. J. W. HARTARY, Assistant Examiner. 

1. IN A METHOD FOR DIRECT ELECTRON BEAM RECORDING OF INFORMATION IN A SHEET-LIKE RECORDING MEDIUM ADAPTED FOR SUBSEQUENT READOUT OF PRERECORDED INFORMATION BY OPTICAL PROJECTION, SAID MEDIUM CONTAINING A BASE SUPPORT LAYER, AN ELECTRON SENSITIVE COMPOSITION LAYER, AND A CONDUCTIVE LAYER POSITIONED ADJACENT ONE FACE OF SAID SUPPORT LAYER AND COMPOSED OF METAL, THE IMPROVEMENT WHICH COMPRISED THE STEPS OF: (A) EXPOSING UNDER VACUUM ONE SURFACE OF SUCH A MEDIUM TO AN ELECTRON BEAM MODULATED WITH INFORMATION TO BE RECORDED WHILE SIMULTANEOUSLY GROUNDING THE CONDUCTIVE LAYER OF SUCH MEDIUM, SAID BEAM HAVING AN ASSOCIATED ENERGY AND RELATIVE MOTION ADAPTED FOR RECORDING SUCH MODULATION IN THE ELECTRON SENSITIVE COMPOSITION LAYER OF SUCH MEDIUM, AND (B) THEREAFTER CONTACTING SAID CONDUCTIVE LAYER WITH AN AQUEOUS ALKALINE LIQUID FOR A TIME SUFFICIENT TO DISSOLVE AND THEREBY REMOVE SUCH LAYER FROM SUCH MEDIUM. 